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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Optimization of fringe-type laser anemometers for turbine engine component testing

The fringe type laser anemometer is analyzed using the Cramer-Rao bound for the variance of the estimate of the Doppler frequency as a figure of merit. Mie scattering theory is used to calculate the Doppler signal wherein both the amplitude and phase of the scattered light are taken into account. The noise from wall scatter is calculated using the wall bidirectional reflectivity and the irradiance of the incident beams. A procedure is described to determine the optimum aperture mask for the probe volume located a given distance from a wall. The expected performance of counter type processors is also discussed in relation to the Cramer-Rao bound. Numerical examples are presented for a coaxial backscatter anemometer. Previously announced in STAR as N84-25019

Seasholtz, R. G.↗
NASA NTRS1984

Spatial variation of stratospheric aerosol acidity and model refractive index - Implications of recent results

Recent experimental results indicate that little or no solid ammonium sulfate is present in background stratospheric aerosols. Other results allow straightforward calculation of sulfuric acid/water droplet properties (acidity, specific gravity, refractive index) as functions of stratospheric temperature and humidity. These results are combined with a variety of latitudinal and seasonal temperature and humidity profiles to obtain corresponding profiles of droplet properties. These profiles are used to update a previous model of stratospheric aerosol refractive index. The new model retains the simplifying approximation of vertically constant refractive index in the inner stratosphere, but has sulfuric acid/water refractive index values that significantly exceed the previously used room temperature values. Mean conversion ratios (e.g., extinction-to-number, backscatter-to-volume) obtained using Mie scattering calculations with the new refractive indices are very similar to those obtained for the old indices, because the effects of deleting ammonium sulfate and increasing acid indices tend to cancel each other.

Russell, P. B.↗
NASA NTRS1985

Water-ice Clouds on Mars: Location and Seasonal Variation

Water-ice clouds were located on Mars using Viking infrared thermal mapper (IRTM) broadband spectral observations. The IRTM instrument had 5 thermal bands centered at 7, 9, 11, 15, and 20 microns. Clouds and hazes were consistently observed in four northern hemisphere regions centered over Tharsis, Arabia, Elysium, and along the boundary between the crater uplands and the northern plains. During the northern spring and summer when the atmosphere is relatively free of dust, there is a distinct difference between the cloud abundance in the Northern and Southern Hemispheres, with clouds and hazes being rare in the south. A second important class of water-ice clouds are those observed along the boundary of the retreating north polar cap. These clouds occur at all longitudes around the cap and are generally confined to within +/- 5 deg of the cap boundary. The cloud opacities can be estimated using a delta-Eddington radiative transfer model which incorporates Mie scattering and the electrical properties of water-ice. Assuming realistic, but non-unique, values for the ice particle size and cloud temperature, the derived opacities range from near-zero to 1.

Christensen, P. R.↗
NASA NTRS1985

Measurements in the flow field of a cylinder with a laser transit anemometer and a drag rake in the Langley 0.3 m transonic cryogenic tunnel

An experiment was conducted at the 0.3 m Transonic Cryogenic Tunnel using a Laser Transit Anemometer (LTA) to probe the flow field around a 3.05 centimeter-diameter circular cylinder. Measurements were made along the stagnation line and determination of particle size was evaluated by their ability to follow the flow field. The LTA system was also used to scan into the boundary layer near the 45 degree point on the model. Results of these scans are presented in graphic and tabular form. Flow field particle seeding was accomplished by inbleeding dry service air. The residual moisture (5-10 ppm) condensed and formed ice particles which served as Mie scattering centers for the LTA detection system. Comparison of data taken along the stagnation streamline with theory indicated that these particles tracked the velocity gradient of the flow. Tunnel operating conditions for the tests were a Mach number of 0.3, a pressure of 1.93 x 100000 n/m squared, and a temperature of 225 degrees K. Free stream Mach number and pressure were varied for the particle size determination.

Honaker, W. C.↗
NASA NTRS1982

Macrostructure and microphysics of Saturn's E-ring

Observed optical and infrared properties of Saturn's E-ring are explained in terms of Mie scattering by a narrow distribution of ice spheres with an effective diameter of 2 to 2.5 microns, and an effective variance of 0.1 to 0.15. The spherical shape of the ring particles and their narrow size distribution imply that they had a molten origin, followed by quick freezing. Continued replenishment of the E-ring by volcanic eruptions on Enceladus seems plausible. The vertical structure of the E-ring consists of many layers. The stratification of the particles may be due to electrostatic levitation, similar to that experienced by particles in the spokes.

Pang, K. D.↗
NASA NTRS1984

The E ring of Saturn and satellite Enceladus

Photographic imagery from Pioneer and Voyager flyby satellites has been used to study the microphysical properties of Saturn's outermost E-ring, and to determine the physical relationship between the E-ring and the satellite Enceladus. The optical and infrared characteristics of the E-ring are explained in terms of Mie scattering of ice spheres with an effective diameter of 2 to 2.25 microns and an effective variance of 0.1 to 1.5. It is suggested that the E-ring is continuously replenished by volcanic eruptions on Enceladus, and recent tectonic evidence is cited in support of this hypothesis. A number of similarities in the relationship between the E-ring and Enceladus and Io and its torus are discussed, within the framework of a general model of outer solar system volcanism and planetary ring interaction.

Pang, K. D.↗
NASA NTRS1986

Vertical structure of Arctic haze observed by lidar

In the study of the Arctic Haze phenomenon, understanding the vertical structure of the haze aerosol is crucial in defining mechanisms of haze transport. Questions have also arisen concerning the representativeness of surface observations of Arctic Haze. Due to the strongly stratified nature of the Arctic troposphere, the mechanisms which transport aerosol to the surface from the transport altitudes of the lower troposphere are not obvious. In order to examine these questions, a Mie scattering lidar was installed at Alert, NWT, Canada. Lidar observes atmospheric aerosols and hydrymeteors as they appear in nature, unmodified by sampling effects. As such the results obtained are more realistic of the light scattering characteristics of the in situ aerosol than are those obtained by integrating nephelometers, for example, which heat the aerosol and dry it before measurement. With this lidar, a pulse was transmitted vetically through an evacuated tube in the roof of a building at Alert. The receiver consisted of a 20cm diameter Fresnel telescope, neutral density and polarizing filters, and RCA C31000A PMT, Analog Modules LA-90-P logarithmic amplifier and a Lecroy TR8827 32 MHz digitizer. The lidar equation was solved for the backscattering coefficient of the aerosol assuming no two way transmission losses in the signal. The lidar results have shown that intercomparison between lidar obtained visibilities and observer visibilities are in much better agreement than for other optical or aerosol monitors. Three new effects were identified in the lidar profiles which contribute to the vertical transport of haze. These effects are briefly discussed.

Hoff, R. M.↗
NASA NTRS1986

The 3.1 micrometer ice band in infrared reflection nebulae

Recent observations show that infrared reflection nebulae are common phenomena in star forming regions. Extensive observations were made of two nearby infrared reflection nebulae, Orin Molecular Cloud 2 IRS1 (OMC-2/IRS1) and Cepheus A IRS6a (Cep-A/IRS6a). Mie scattering models of ice coated grains were used to study the constraints on the properties and locations of grains that could produce a feature similar to that observed in OMC-2 and Cep-A. It was concluded that scattering by ice particles alone could not be responsible for the 3.1 micron feature observed in infrared reflection nebulae.

Pendleton, Y.↗
NASA NTRS1987

University of Missouri-Rolla cloud simulation facility - Proto II chamber

The design and supporting systems for the cooled-wall expansion cloud chamber, designated Proto II, are described. The chamber is a 10-sided vertical cylinder designed to be operated with interior wall temperatures between +40 and -40 C, and is to be utilized to study microphysical processes active in atmospheric clouds and fogs. Temperatures are measured using transistor thermometers which have a range of + or - 50 C and a resolution of about + or - 0.001 C; and pressures are measured in the chamber by a differential strain gauge pressure transducer. The methods used for temperature and pressure control are discussed. Consideration is given to the chamber windows, optical table, photographic/video, optical attenuation, Mie scattering, and the scanning system for the chamber. The system's minicomputer and humidifier, sample preparation, and chamber flushing are examined.

White, Daniel R.↗
NASA NTRS1988

Radiative aspects of Antarctic ozone hole in 1985

In order to investigate the radiative heating effects of aerosols during September - October, 1985, at Antarctica, researchers solved the radiative transfer equation using a one-dimensional model, which includes the absorption of solar energy by water vapor, carbon dioxide, ozone and aerosols, the thermal emission and absorption by the above species and in addition, Rayleigh and Mie scattering, and the surface scattering effects. In this calculation, they used data of ozone density, water vapor density and aerosol extinction at 0.385, 0.453, 0.525 and 1.02 mu m in the stratosphere obtained by SAGE II satellite and meteorological data from NOAA. Results show that the Antarctic stratosphere is nearly in radiative equilibrium during that period, if the effects of aerosols are excluded. It is also shown that the heating effects of aerosols are too small to cause effective upward motions, in spite of some ambiguous parameters such as aerosol composition. The parameter dependences of results are also discussed.

Akiyoshi, H.↗
NASA NTRS1989

Fresnel diffraction by spherical obstacles

Lommel functions were used to solve the Fresnel-Kirchhoff diffraction integral for the case of a spherical obstacle. Comparisons were made between Fresnel diffraction theory and Mie scattering theory. Fresnel theory is then compared to experimental data. Experiment and theory typically deviated from one another by less than 10 percent. A unique experimental setup using mercury spheres suspended in a viscous fluid significantly reduced optical noise. The major source of error was due to the Gaussian-shaped laser beam.

Hovenac, Edward A.↗
NASA NTRS1990

Lidar instruments proposed for Eos

Lidar, an acronym for light detection and ranging, represents a class of instruments that utilize lasers to send probe beams into the atmosphere or onto the surface of the Earth and detect the backscattered return in order to measure properties of the atmosphere or surface. The associated technology has matured to the point where two lidar facilities, Geodynamics Laser Ranging System (GLRS), and Laser Atmospheric Wind Sensor (LAWS) were accepted for Phase 2 studies for Eos. A third lidar facility Laser Atmospheric Sounder and Altimeter (LASA), with the lidar experiment EAGLE (Eos Atmospheric Global Lidar Experiment) was proposed for Eos. The generic lidar system has a number of components. They include controlling electronics, laser transmitters, collimating optics, a receiving telescope, spectral filters, detectors, signal chain electronics, and a data system. Lidar systems that measure atmospheric constituents or meteorological parameters record the signal versus time as the beam propagates through the atmosphere. The backscatter arises from molecular (Rayleigh) and aerosol (Mie) scattering, while attenuation arises from molecular and aerosol scattering and absorption. Lidar systems that measure distance to the Earth's surface or retroreflectors in a ranging mode record signals with high temporal resolution over a short time period. The overall characteristics and measurements objectives of the three lidar systems proposed for Eos are given.

Grant, William B.↗
NASA NTRS1990

The radiation budget of stratocumulus clouds measured by tethered balloon instrumentation: Variability of flux measurements

Measurements of longwave and shortwave radiation were made using an instrument package on the NASA tethered balloon during the FIRE Marine Stratocumulus experiment. Radiation data from two pairs of pyranometers were used to obtain vertical profiles of the near-infrared and total solar fluxes through the boundary layer, while a pair of pyrgeometers supplied measurements of the longwave fluxes in the cloud layer. The radiation observations were analyzed to determine heating rates and to measure the radiative energy budget inside the stratocumulus clouds during several tethered balloon flights. The radiation fields in the cloud layer were also simulated by a two-stream radiative transfer model, which used cloud optical properties derived from microphysical measurements and Mie scattering theory.

Duda, David P.↗
NASA NTRS1990

Release of liquid water from the Space Shuttle

Groundbased and onboard video images of a sunlit Shuttle Orbiter water dump are interpreted as showing that the continuous 1-mm-diameter liquid stream quickly breaks up in near-vacuum to form ice/snow particles of two characteristic sizes. Discrete large droplets are most evident in the close-in photographs, and unresolved submicron 'fog' from recondensation of overexpanded evaporated water appears to dominate the ground-telescope photographs of the 2.5 km long optically detectable trail. The mean diameter of the smaller particles was estimated from the spatial distribution of visible radiance using a model of their energy balance, (small) surface roughening as they sublime, and Mie scattering of pre-dawn sunlight. The results are consistent with those from recent space-tank simulations.

Pike, C. P.↗
NASA NTRS1990

Relationship of radar cross section to the geometric size of orbital debris

An accurate determination of the sizes of orbiting debris objects is essential to predicting collision rates, atmospheric decay rates, and fragmentation laws for orbiting objects. The radar cross section (RCS) is the most common means of estimating the size of orbiting objects. However, the RCS is prone to error due to Mie scattering, compositional effects, geometrical effects, tumbling, and other dependencies. Optical measurement methods are theoretically much more accurate, but necessitate estimates of the object's albedo. This paper examines the relationship of RCS and optical cross section to physical size and albedo, and presents rules useful for quantizing the physical size of space objects.

Badhwar, Gautam D.↗
NASA NTRS1991

Experimental study of cross-stream mixing in a cylindrical duct

An experimental investigation of cross stream injection and mixing was conducted with application to a low NO sub x combustor for the High Speed Civil Transport (HSCT). Mixing in a cylindrical chamber was studied for transverse injection from slanted slot and round orifice injectors. Momentum ratio, density ratio, and number were studied. Quantitative measurement of injectant concentration distributions were obtained by planar digital imaging of the Mie scattered light from an aerosol seed uniformly mixed with the injectant. The unmixedness, defined as the ratio of the r.m.s. concentration fluctuation to mean concentration in a plane perpendicular to the main flow direction, was found to be primarily a function of momentum ratio and injector spacing. An optimum spacing is indicated. Unmixedness is also a function of orifice size, or mass flow ratio, but the mass flow dependence can be accounted for by normalizing the unmixedness with its maximum theoretical value. The data indicate that a density ratio greater than unity retards mixing. It was found that above a certain momentum flux ratio, mixing with slanted slot injectors was better than with round hole injectors.

Vranos, A.↗
NASA NTRS1989

Physical retrieval of precipitation cell parameters using passive 118-GHz observations

Physical retrieval of precipitation parameters from 118-GHz spectra is investigated using an iterative planar-stratified numerical radiative-transfer model. Liquid and frozen hydrometeors are modeled as spherical Marshall-Palmer and Sekhon-Srivastava (SS) distributed Mie-scattering polydispersions, respectively, with Henyey-Greenstein phase functions. A comparison of 118-GHz rain-cell spectral perturbations observed during Cohmex with model calculations based on coincident radar data yields + or - 10 percent agreement over the convective core region, although a mean ice size 50 percent larger than that given by the SS distribution is required for agreement over the anvil region. A rain-cell model parameterized by top-altitude and total water density suggests that the dominant 118-GHz spectral modes can be used to retrieve top-layer altitude with rms errors of about 1-1.5 km, consistent with statistical retrieval results. Model calculations also suggest that cell density is not observable using 118-GHz spectra alone.

Gasiewski, A. J.↗
NASA NTRS1991

Experimental study of cross-stream mixing in a cylindrical duct

An experimental investigation of cross stream injection and mixing has been conducted with application to a low NO(x) combustor for the HSCT. Mixing in a cylindrical chamber has been studied for transverse injection from slanted slot and round orifice injectors. Momentum ratio, density ratio, and injector geometry were the primary variables. Slanted slots of various size, aspect ratio, and number were studied. Quantitative measurement of injectant concentration distributions were obtained by planar digital imaging of the Mie-scattered light from an aerosol seed uniformly mixed with the injectant. The unmixedness, defined as the ratio of the rms concentration fluctuation to mean concentration in a plane perpendicular to the main flow direction, was found to be primarily a function of momentum ratio and injector spacing. An optimum spacing is indicated. Unmixedness is also a function of orifice size, or mass flow ratio, but the mass flow dependence can be accounted for by normalizing the unmixedness with its maximum theoretical value. The data indicate that density ratio greater than unity retards mixing. It was found that above a certain momentum flux ratio, mixing with slanted slot injectors was better than with round hole injectors.

Vranos, A.↗